Analysis and design of modified deadbeat controller for 3-phase uninterruptible power supply

This paper proposes a modified deadbeat control scheme of 3-phase PWM inverter with LC filter for uninterruptible power supply (UPS). The deadbeat current and voltage controller are used to obtain the fast transient response of the UPS system in general. However, the conventional deadbeat controller has a defect and becomes unstable. In this paper, to remove the defect which makes a system unstable due to the same pole placement of a conventional deadbeat current and voltage controller, modified deadbeat algorithm, which produces a first-order exponential response during one input step, is proposed. Because the overall controller is constructed by deadbeat control, the response of the proposed control system is fast and the structure of the controller is simple. In addition, the full-order state and disturbance observer is constructed to compensate the disturbances generated by a sudden change of load currents. The proposed disturbance observer estimates state values of load currents within a finite time, and cancels the disturbances by adding a feedforward compensation loop in the control system. The validity of the modified deadbeat control scheme is proved by the results of simulation and experiment.